Streetcars (sometimes called light rail or trams) are the new (not that new, really) big thing in public transit systems.
High-floor streetcars are ideal, but difficult to use because you either must have stairs within the train (which fails accessibility requirements, like the old CLRVs in Toronto) or you must have higher platforms on the street (which isn’t well integrated with the streetscape, think the Calgary C-Train).
Low-floor streetcars are accessible, but aren’t ideal precisely because the doors and wheels can’t overlap, so you have less capacity because you have to space out doors more.